Full Report
The UMAS protocol, in its implementation prior to the version in which the CVE-2021-22779 vulnerability was fixed, had significant shortcomings that had a critical effect on the security of control systems based on Schneider Electric controllers.
Analysis Summary
# Vulnerability: Authentication Bypass in Schneider Electric UMAS Protocol
## CVE Details
- **CVE ID:** CVE-2021-22779
- **CVSS Score:** 10.0 (Critical)
- **CWE:** CWE-306 (Missing Authentication for Critical Function) / CWE-287 (Improper Authentication)
## Affected Systems
- **Products:** Schneider Electric Modicon Controllers (M580, M340, MC80, Momentum, Premium, Quantum).
- **Versions:** All firmware versions utilizing the UMAS protocol prior to the remediation releases in 2021/2022.
- **Configurations:** Systems where the "Application Password" feature was either not configured or relied upon for complete session security, and systems where Network Management protection was not enforced.
## Vulnerability Description
The Unified Messaging Application Services (UMAS) protocol is a proprietary layer sitting on top of Modbus (TCP port 502) used for configuring and monitoring Schneider Electric PLCs. The vulnerability stems from a lack of robust authentication and session integrity checks.
Researchers discovered that the "Application Password" provided only a superficial layer of security. An attacker could bypass authentication by intercepting or predicting session identifiers, or by leveraging specific UMAS function codes that did not require prior authentication. This allowed unauthorized remote users to execute privileged commands, such as stopping the PLC, uploading/downloading malicious logic, or modifying memory values.
## Exploitation
- **Status:** PoC Available / Publicly Documented (Detailed reverse-engineering of the protocol and function codes).
- **Complexity:** Medium (Requires knowledge of the proprietary UMAS function codes).
- **Attack Vector:** Network (TCP 502).
## Impact
- **Confidentiality:** High (Ability to read PLC configuration and logic).
- **Integrity:** High (Ability to modify control logic and process parameters).
- **Availability:** High (Ability to stop the controller or initiate a "Cold Start").
## Remediation
### Patches
Schneider Electric released firmware updates for the following families to implement "Application Protection" and enhanced security:
- **Modicon M580:** Update to v3.20 or higher.
- **Modicon M340:** Update to v3.30 or higher.
- **Modicon Quantum & Premium:** Transition to newer hardware or apply latest security notifications.
### Workarounds
- **Network Segmentation:** Isolate ICS/SCADA networks from the corporate network and the internet.
- **Access Control:** Implement Access Control Lists (ACLs) on the PLC settings to restrict UMAS/Modbus communication to authorized Engineering Workstations (EWS) only.
- **Hardening:** Disable unused services and protocols (e.g., FTP, HTTP, SNMP) within the PLC configuration.
## Detection
- **Indicators of Compromise:** Unusual UMAS function codes originating from unauthorized IP addresses. Repeated "Initialize" or "Take Reserve" commands (Function codes 0x10, 0x1C).
- **Detection Methods:**
- Use Deep Packet Inspection (DPI) capable firewalls or IDS (e.g., Snort/Suricata) to monitor TCP port 502.
- Monitor for UMAS command `0x58` (Release Reservation) followed by unauthorized writes.
- Analysis of PLC logs for unexpected transition to "STOP" mode.
## References
- **Vendor Advisory:** hxxps[://]www[.]se[.]com/ww/en/download/document/SEVD-2021-194-01/
- **Kaspersky ICS CERT Analysis:** hxxps[://]ics-cert[.]kaspersky[.]com/publications/reports/2022/09/29/the-secrets-of-schneider-electrics-umas-protocol/
- **NVD:** hxxps[://]nvd[.]nist[.]gov/vuln/detail/CVE-2021-22779